Sphenacodontoids Temporal range: Late Carboniferous-Recent, 300–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Fossilized skull of two sphenacodontoids: Clelandina (Therapsida, Gorgonopsidae) and a Dimetrodon (Sphenacodontidae).
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Clade:	Sphenacomorpha
Clade:	Sphenacodontia
Clade:	Pantherapsida
Clade:	Sphenacodontoidea Marsh, 1878
Clades
†Shashajaia †Sphenacodontidae Therapsida

Sphenacodontoidea is a node-based clade that is defined to include the most recent common ancestor of Sphenacodontidae and Therapsida and its descendants (including mammals).^[1] Sphenacodontoids are characterised by a number of synapomorphies concerning proportions of the bones of the skull and the teeth.^[2][3]

The sphenacodontoids evolved from earlier sphenacodonts such as Haptodus and Ianthodon via a number of transitional stages of small, 1-10 kg, faunivore animals.^[1] The possible common ancestor of sphenacodontids and therapsids was a carnivorous synapsid that reached moderate or large size and more closely resembled the land-dominant Early Permian sphenacodontids than the small Haptodus.^[2] The first predators among Sphenacodontoidea, like Shashajaia, appeared in the tropical western part of Pangea in the Late Carboniferous.^[1] Later, in Permian, sphenacodontoids gave rise to the dominant terrestrial carnivores in both sphenacodontid and therapsid groups.^[2]

The following taxonomy follows Fröbisch et al. (2011) and Benson (2012) unless otherwise noted.^[4][5]

Class Synapsida

• Sphenacodontoidea
  • Family †Sphenacodontidae
  • Therapsida

Sphenacodontoidea in a cladogram modified from Huttenlocker et al. (2021):^[1]

• Evolution of mammals

• Laurin, M. and Reisz, R. R., 1997, Autapomorphies of the main clades of synapsids - Tree of Life Web Project

• "Synapsida". Mikko's Phylogeny Archive. Archived from the original on September 3, 2007.

v t e Synapsida
Kingdom: Animalia Phylum: Chordata Superclass: Tetrapoda Clade: Amniota Tetrapodomorpha see Tetrapodomorpha Reptiliomorpha see Reptiliomorpha Synapsida see below↓
Synapsida Synapsida †Diadectomorpha? †Caseasauria? Eothyrididae Asaphestera? Eothyris Oedaleops Vaughnictis Caseidae Alierasaurus Angelosaurus Arisierpeton Callibrachion Casea Caseoides Caseopsis Cotylorhynchus Datheosaurus Ennatosaurus Eocasea Euromycter Lalieudorhynchus Martensius Oromycter Phreatophasma Ruthenosaurus Trichasaurus Eupelycosauria †Varanopidae? Apsisaurus Archaeovenator Ascendonanus Eoscansor Dendromaia Nitosaurus? Pyozia Thrausmosaurus Mesenosaurinae Anningia Cabarzia Elliotsmithia Heleosaurus Mesenosaurus Microvaranops Varanodontinae Aerosaurus Mycterosaurus? Ruthiromia Tambacarnifex Varanops Varanodon Watongia Metopophora see below↓ Incertae sedis †Dimacrodon †Driveria †Gorgodon †Knoxosaurus †Mastersonia †Protoclepsydrops?
Metopophora †Ophiacodontidae Archaeothyris Baldwinonus Clepsydrops Echinerpeton Ophiacodon Stereophallodon Stereorhachis Varanosaurus Haptodontiformes †Ianthodon †Milosaurus †Edaphosauridae Bohemiclavulus Edaphosaurus Glaucosaurus Gordodon Ianthasaurus Lupeosaurus Melanedaphodon Ramodendron Remigiomontanus Xyrospondylus Sphenacodontia †Cutleria †Haptodus †Hypselohaptodus †Kenomagnathus †Tetraceratops †Palaeohatteriidae Palaeohatteria Pantelosaurus Sphenacodontoidea †Shashajaia †Sphenacodontidae Cryptovenator Ctenorhachis Ctenospondylus Cutleria? Dimetrodon Eosyodon Macromerion Neosaurus Secodontosaurus Sphenacodon Steppesaurus? Tappenosaurus? Tetraceratops? Therapsida see below↓
Therapsida Therapsida †Raranimus †Biarmosuchia see Biarmosuchia †Dinocephalia see Dinocephalia †Anomodontia see Anomodontia includes dicynodonts †Gorgonopsia see Gorgonopsia Eutheriodontia †Therocephalia see Therocephalia Cynodontia see Cynodontia includes mammals Incertae sedis †Dinosaurus †Kamagorgon †Niaftasuchus
See also: Pelycosauria Phthinosuchia Theriodontia Category